1. Field of the Invention
The present invention relates to an electrostatic actuator vibrating by electrostatic force, a method of producing such an electrostatic actuator, an electrostatic micropump including such an electrostatic actuator, an ink jet recording head including such an electrostatic actuator and ejecting an ink droplet by a pressure wave caused by electrostatic force, an ink jet recording apparatus including such an ink jet recording head, a liquid droplet ejecting head, an ink cartridge including such a liquid droplet ejecting head, an ink jet recording apparatus including such a liquid droplet ejecting head, and a method of producing such a liquid droplet ejecting head.
2. Description of the Related Art
Products to which an electrostatic actuator is applied include an electrostatic micropump and a drop-on-demand ink jet recording head.
As methods of driving a micropump for transporting liquid, there have been disclosed a piezoelectric method using piezoelectric effect, a thermal method utilizing liquid expansion caused by heat, and an electrostatic driving method employing electrostatic attraction. Among those methods, the electrostatic driving method have the advantage of low power consumption due to its use of electrostatic force, and a micropump using this method is easy to make fine in size by means of a processing technique using a silicon device processing technique.
However, since such a micropump employs silicon as a material of its components, the silicon may be eluted from the components depending on the nature of the transported liquid of alkalinity or acidity, thus causing damage to the micropump. Therefore, it is commonly practiced to form an anti-corrosive film on a surface of the silicon which surface contacts the liquid. A description will be given below of ink jet recording heads in which this anti-corrosive film is formed.
There have been proposed a variety of methods of driving an ink jet recording head for an ink jet recording apparatus which ink jet recording head uses an electrostatic actuator which performs recording by ejecting an ink droplet through a nozzle hole directly onto a recording medium.
WO98/42513 discloses an ink jet recording head for a print head employed in a drop-on-demand ink jet recording apparatus in which ink jet recording head an anti-corrosive thin film of Ti, a Ti compound, and Al2O3 having resistance to ink is formed on the surface of a diaphragm forming an ink pressure chamber for pressurizing and ejecting ink.
Japanese Laid-Open Patent Application No. 10-291322 discloses a method of producing an ink jet head which method includes the steps of forming a silicon oxide film on the surface of a diaphragm forming an ink pressure chamber for pressurizing and ejecting ink, and thereafter forming in layers ink-resistant films of oxide, nitride, and a metal to close pinholes in the diaphragm.
Such a diaphragm of an electrostatic actuator which diaphragm is formed by a single or a plurality of layers of ink-resistant anti-corrosive thin films of Ti, a Ti compound, Al2O3, and a silicon oxide suffers a decrease in a yield due to corrosion, a malfunction caused by a deflection of the diaphragm generated by buckling, and a breakage caused by mishandling during the production thereof, thus resulting in an increase in the production costs of the electrostatic actuator.
When such an electrostatic actuator including a diaphragm formed by a single or a plurality of layers of ink-resistant anti-corrosive thin films of Ti, a Ti compound, Al2O3, and a silicon oxide is applied to an electrostatic micropump, an ink jet recording head, or an ink jet recording apparatus, the internal stress of the anti-corrosive thin films and a film thickness distribution on the diaphragm cause the diaphragm to buckle to have a deflection. The deflection of the diaphragm causes an increase in a driving voltage, which leads to an increase in the costs of a driving circuit and greater variations in the driving voltage, thus causing an increase in power consumption. Further, the deflection of the diaphragm causes differences in an ejection characteristic among bits at a time of ejecting liquid or ink, poor liquid or ink ejection, and certain corrosion depending on a type of liquid or ink.
Such a conventional method of producing, for instance, an electrostatic micropump, an ink jet recording head, or an ink jet recording apparatus separately produces a first silicon substrate of approximately 200 xcexcxcexcm in thickness having liquid or ink chambers and diaphragms of a few microns in thickness formed therein and a second silicon substrate having n+ or p+-type impurity diffusion driving electrodes formed therein, and bonds the first and second silicon substrates directly. In this process, the first silicon substrate may be damaged by mishandling, thus reducing a production yield.
Further, an ink jet recording apparatus employed as an image recording apparatus (an imaging apparatus) such as a printer, a facsimile machine, a copying machine, or a plotter includes an ink jet head as a liquid droplet ejecting head including nozzles for ejecting ink droplets, ink channels (also referred to as ejection chambers, pressure chambers, liquid pressure chambers, or liquid chambers) with which the nozzles communicate, and driving means for pressurizing ink in the ink channels. The liquid droplet ejecting heads include, for instance, those for ejecting liquid resist or DNA specimens as liquid droplets, but a description given below will focus mainly on an ink jet head.
As an ink jet head, known is a piezoelectric ink jet head that ejects ink droplets by changing the capacities of ink channels by deforming diaphragms forming wall faces of the ink channels by using piezoelectric elements as energy generation means for generating energy for pressurizing ink in the ink channels. Further, a so-called bubble type ink jet head that ejects ink droplets by means of pressures produced by generating air bubbles by heating ink in ink channels using calorific resistances is also known. Moreover, Japanese Laid-Open Patent Application No. 6-71882 discloses an electrostatic ink jet head that ejects ink droplets by changing the volumes of ink channels by deforming diaphragms forming wall faces of the ink channels by means of electrostatic forces generated between the diaphragms and electrodes that are arranged to oppose each other.
In order for an ink jet recording apparatus to record, particularly, a color image with high quality at a high speed, in terms of achieving high quality, high-density processing using a micromachine technique is employed to produce the ink jet recording apparatus and a material for head components has shifted from a metal or plastic to silicon, glass, or ceramics with the silicon being particularly employed as a material preferable for fine processing.
Further, in terms of colorization, efforts have been made mainly to develop ink and recording media. The development of ink ingredients and components has been promoted to optimize permeability, coloring, and a color mixture prevention characteristic of ink when the ink adheres to a recording medium and to increase long-term preservability of a printed medium and preservability of the ink itself.
In this case, the ink may dissolves the head components depending on a combination of the ink and a material for the head components. Particularly, in the case of forming a channel formation member of silicon, the silicon is dissolved in the ink to be deposited on nozzle parts so that nozzles are clogged or coloring of the ink is deteriorated to degrade quality of image. Further, in the case of a head using diaphragms, if the diaphragms are formed of silicon thin films and silicon is dissolved in the ink, the vibration characteristic of the diaphragms is altered or the diaphragms are prevented from vibrating.
In this case, it often makes it difficult to perform high-density processing or decrease processing accuracy to cope with the above-described problems by changing the material for the head components. Further, the change of the material requires a great change in processing steps or an improvement in a fabrication process, thus causing a decrease in nozzle density and further, a decrease in print quality.
On the other hand, in the case of coping with the above-described problems by adjusting the component of the ink, the image quality may be deteriorated since the component or ingredients of the ink is originally adjusted, for increasing print quality, to optimize the permeability and coloring of the ink with respect to a recording medium or to increase the preservability of the ink and a printed medium.
Therefore, in a conventional ink jet head, an ink-resistant thin film is formed on the ink-contacting surface of a channel formation member which surface contacts ink as disclosed in the above-described WO/98/42513 and Japanese Laid-Open Patent Application No. 10-291322. Further, Japanese Laid-Open Patent Application No. 5-229118 discloses an ink jet head in which an oxide film is formed on the ink-contacting surfaces of its components.
However, in the conventional ink jet head, an inorganic ink-resistant film includes an area that electrochemically easily dissolves depending on the pH of ink, therefore resulting in strict requirements for the ink. Specifically, a silicon oxide film, for instance, which easily dissolves in ink having a pH larger than nine, is required to have a considerable thickness to increase resistance to ink since ink of a good coloring characteristic is normally alkaline having a pH of approximately 10 to 11. The formation of a thick inorganic film often entails difficulties in its process and causes the problem of deformation of the channel formation member due to the generation of an internal stress.
Further, according to sputtering or evaporation employed in forming an ink-resistant film, particles for forming the thin film have their directions. Therefore, the thin film becomes partially thin or is totally prevented from being formed due to the shaded parts of channels resulting from their structures, thus making it difficult to coat the entire surface completely with the thin film.
It is a general object of the present invention to provide an electrostatic actuator vibrating by electrostatic force, a method of producing such an electrostatic actuator, an electrostatic micropump including such an electrostatic actuator, an ink jet recording head including such an electrostatic actuator and ejecting an ink droplet by a pressure wave caused by electrostatic force, an ink jet recording apparatus including such an ink jet recording head, a liquid droplet ejecting head, an ink cartridge including such a liquid droplet ejecting head, an ink jet recording apparatus including such a liquid droplet ejecting head, and a method of producing such a liquid droplet ejecting head in which the above-described disadvantages are eliminated.
A more specific object of the present invention is to provide: an electrostatic actuator that prevents a diaphragm on which an anti-corrosive thin film is formed from buckling, deflecting, and malfunctioning, has good protection against liquid or ink, has an increased yield, is producible at low costs and energy-saving with low power consumption, reduces differences in liquid or ink ejections, and records an ink image of high quality; a method of producing such an electrostatic actuator; an electrostatic micropump including such an electrostatic actuator; an ink jet recording head including such an electrostatic actuator; and an ink jet recording apparatus including such an ink jet recording head.
Yet another more specific object of the present invention is to provide a highly reliable liquid droplet ejecting head and head-integrated ink cartridge producible at low costs and free of corrosion, a highly reliable ink jet recording apparatus including such a liquid droplet ejection head or ink cartridge, and a method of producing such a liquid droplet ejecting head on which a highly reliable liquid-resistant thin film is formed at low costs.
The above objects of the present invention are achieved by an electrostatic actuator including a diaphragm caused to vibrate by electrostatic force, an electrode substrate opposing the diaphragm, an electrode formed on the electrode substrate so as to oppose the diaphragm with a gap being formed between the electrode and the diaphragm, an anti-corrosive thin film formed on the diaphragm, and diaphragm deflection prevention means preventing the diaphragm from deflecting.
The above-described electrostatic actuator prevents the diaphragm on which the anti-corrosive thin film is formed from buckling, deflecting, and malfunctioning by the deflection prevention means, has good protection or anti-corrosiveness against liquid or ink, has an increased yield, and is producible at low costs.
The above objects of the present invention are also achieved by a method of producing an electrostatic actuator including a diaphragm caused to vibrate by electrostatic force, an electrode substrate opposing the diaphragm, an electrode formed on the electrode substrate so as to oppose the diaphragm with a gap being formed between the electrode and the diaphragm, an anti-corrosive thin film formed on the diaphragm, and diaphragm deflection prevention means preventing the diaphragm from deflecting, which method includes the steps of (a) joining a first substrate in which a diaphragm is formed and a second substrate on which an electrode is formed, and (b) forming an anti-corrosive thin film on the diaphragm after the step (a).
According to the above-described method, the electrostatic actuator preventing the diaphragm on which the anti-corrosive thin film is formed from buckling, deflecting, and malfunctioning by the deflection prevention means, having good protection or anti-corrosiveness against liquid or ink, and having an increased yield is producible at low costs.
The above objects of the present invention are also achieved by an electrostatic micropump including a nozzle hole for ejecting a liquid droplet, a liquid chamber that is a liquid channel communicating with the nozzle, and an electrostatic actuator forming wall faces of the liquid chamber, the electrostatic actuator including a diaphragm caused to vibrate by electrostatic force, an electrode substrate opposing the diaphragm, an electrode formed on the electrode substrate so as to oppose the diaphragm with a gap being formed between the electrode and the diaphragm, an anti-corrosive thin film formed on the diaphragm, and diaphragm deflection prevention means preventing the diaphragm from deflecting, wherein the liquid droplet is ejected by a pressure wave generated by the electrostatic force.
The above-described electrostatic micropump includes the electrostatic actuator that prevents the diaphragm on which the anti-corrosive thin film is formed from buckling, deflecting, and malfunctioning by the deflection prevention means, has good protection or anti-corrosiveness against liquid or ink, has an increased yield, is producible at low costs and energy-saving with low power consumption, and realizes a stable liquid ejection characteristic.
The above objects of the present invention are also achieved by an ink jet recording head including a nozzle hole for ejecting an ink droplet, an ink chamber that is an ink channel communicating with the nozzle, and an electrostatic actuator forming wall faces of the ink chamber, the electrostatic actuator including a diaphragm caused to vibrate by electrostatic force, an electrode substrate opposing the diaphragm, an electrode formed on the electrode substrate so as to oppose the diaphragm with a gap being formed between the electrode and the diaphragm, an anti-corrosive thin film formed on the diaphragm, and diaphragm deflection prevention means preventing the diaphragm from deflecting, wherein the ink droplet is ejected by a pressure wave generated by the electrostatic force.
The above-described ink jet head includes the electrostatic actuator that prevents the diaphragm on which the anti-corrosive thin film is formed from buckling, deflecting, and malfunctioning by the deflection prevention means, has good protection or anti-corrosiveness against liquid or ink, has an increased yield, is producible at low costs and energy-saving with low power consumption, and realizes a stable ink ejection characteristic.
The above objects of the present invention are also achieved by an ink jet recording apparatus including a conveying part for conveying a recording medium on which an ink image is recorded, and an ink jet recording head for recording the ink image on the recording medium by ejecting ink thereon, the ink jet recording head including a nozzle hole for ejecting ink, an ink chamber that is an ink channel communicating with the nozzle, and an electrostatic actuator forming wall faces of the ink chamber, the electrostatic actuator including a diaphragm caused to vibrate by electrostatic force, an electrode substrate opposing the diaphragm, an electrode formed on the electrode substrate so as to oppose the diaphragm with a gap being formed between the electrode and the diaphragm, an anti-corrosive thin film formed on the diaphragm, and diaphragm deflection prevention means preventing the diaphragm from deflecting, wherein the ink is ejected by a pressure wave generated by the electrostatic force.
The above-described ink jet recording apparatus includes the electrostatic actuator that prevents the diaphragm on which the anti-corrosive thin film is formed from buckling, deflecting, and malfunctioning by the deflection prevention means, has good protection or anti-corrosiveness against liquid or ink, has an increased yield, is producible at low costs and energy-saving with low power consumption, and realizes a stable liquid ejection characteristic. Therefore, the ink jet recording apparatus realizes high-quality image recording.
The above objects of the present invention are also achieved by a liquid droplet ejecting head including a channel formation member including liquid channels for containing liquid and partition walls separating the liquid channels, nozzles communicating with the liquid channels, and a liquid-resistant thin film formed on liquid-contacting surfaces of the liquid channels, the surfaces contacting the liquid, the liquid-resistant thin film having resistance to the liquid and including an organic resin film, wherein the liquid in the liquid channels is pressurized to be ejected from the nozzles as liquid droplets.
According to the above-described liquid droplet ejecting head, corrosion caused by liquid can be prevented at low costs, thus increasing reliability.
The above objects of the present invention are also achieved by an ink cartridge including an ink jet head, the ink jet head including a channel formation member including ink channels for containing ink, nozzles communicating with the ink channels, and an ink-resistant thin film formed on ink-contacting surfaces of the ink channels, the surfaces contacting the ink, the ink-resistant thin film having resistance to the ink and including an organic resin film, wherein the ink in the ink channels is pressurized to be ejected from the nozzles as ink droplets, and an ink tank for supplying the ink to the ink jet head, the ink tank being formed integrally with the ink jet head.
The above-described ink cartridge, which includes the above-described ink jet head, is free of nozzle clogging, thereby increasing reliability.
The above objects of the present invention are also achieved by an ink jet recording apparatus including an ink jet head, the ink jet head including a channel formation member including ink channels for containing ink, nozzles communicating with the ink channels, and an ink-resistant thin film formed on ink-contacting surfaces of the ink channels, the surfaces contacting the ink, the ink-resistant thin film having resistance to the ink and including an organic resin film, wherein the ink in the ink channels is pressurized to be ejected from the nozzles as ink droplets.
The above objects of the present invention are also achieved by an ink jet recording apparatus including an ink cartridge, the ink cartridge including an ink jet head, the ink jet head including a channel formation member including ink channels for containing ink, nozzles communicating with the ink channels, and an ink-resistant thin film formed on ink-contacting surfaces of the ink channels, the surfaces contacting the ink, the ink-resistant thin film having resistance to the ink and including an organic resin film, wherein the ink in the ink channels is pressurized to be ejected from the nozzles as ink droplets, and an ink tank for supplying the ink to the ink jet head, the ink tank being formed integrally with the ink jet head.
The above-described ink jet recording apparatuses include the ink jet head and the ink cartridge according to the present invention, thus realizing highly reliable and stable recording with increased image quality.
The above objects of the present invention are also achieved by a method of producing a liquid droplet ejecting head including a channel formation member including liquid channels for containing liquid, nozzles communicating with the liquid channels, and a liquid-resistant thin film formed on liquid-contacting surfaces of the liquid channels, the surfaces contacting the liquid, the liquid-resistant thin film having resistance to the liquid and including an organic resin film, the liquid in the liquid channels being pressurized to be ejected from the nozzles as liquid droplets, the method including the step of applying a liquid material for forming the organic resin film on the channel formation member by a spray method.
According the above-described method, the organic resin film serving as the liquid-resistant thin film is producible at low costs by a spray method.
The above objects of the present invention are also achieved by a method of producing a liquid droplet ejecting head including a channel formation member including liquid channels for containing liquid, nozzles communicating with the liquid channels, and a liquid-resistant thin film formed on liquid-contacting surfaces of the liquid channels, the surfaces contacting the liquid, the liquid-resistant thin film having resistance to the liquid and including an organic resin film, the liquid in the liquid channels being pressurized to be ejected from the nozzles as liquid droplets, the organic resin film being a polyimide-based film, the method including the step of (a) applying a solution of a polyamide acid of a viscosity of 20 cP or less on the channel formation member, the polyamide acid being a precursor of polyimide, and (b) forming the polyamide acid into a thin film in a process of heating and dehydrating the polyamide acid into an imide.
According to the above-described method, the organic resin film is producible without pinholes.
The above objects of the present invention are also achieved by a method of producing a liquid droplet ejecting head including a channel formation member including liquid channels for containing liquid, nozzles communicating with the liquid channels, and a liquid-resistant thin film formed on liquid-contacting surfaces of the liquid channels, the surfaces contacting the liquid, the liquid-resistant thin film having resistance to the liquid and including an organic resin film, the liquid in the liquid channels being pressurized to be ejected from the nozzles as liquid droplets, the organic resin film being a polyimide-based film, the method including the step of forming the polyimide thin film by performing heating and evaporation deposition under high vacuum.
According to the above-described method, the organic resin film is producible with uniform quality.